[c-nsp] BGP Regex to allow ISP customers

[Nick Cutting]

Good Afternoon Masters of the BGP,

I am not good at BGP regex.

I need to come up with an ip as-path access-list that will only accept customer routes that belong to a certain provider, the ISP in question does not have a way of differentiating, so I was hoping to use a regex.

So for example if the server provider has an AS of 100, I need to be able to accept all routes originating from 100 (for their customers that do not have BGP) and all routes that have originated from a customer AS, that is a customer of the ISP in question.  The tricky part is if that client is prepending their AS.

e.g.
If 55 and 56 are Customer AS's connected to AS 100 (our ISP)
need to allow:

100 55 i
100 56 i

Or 100 55 55 55 I (to allow for prepending)

But NOT

100 55 something else

Is this possible?
Any help greatly appreciated.

Nick